The shell structure of superheavy nuclei is investigated within various
parametrizations of relativistic and nonrelativistic nuclear mean field models.
The heaviest known even-even nucleus 264Hs is used as a benchmark to estimate
the predictive value of the models. From that starting point, doubly magic
spherical nuclei are searched in the region Z=110-140 and N=134-298. They are
found at (Z=114, N=184), (Z=120, N=172), or at (Z=126, N=184), depending on the
parametrization.Comment: 16 pages RevTeX, 2 tables, 2 low resolution Gif figures (high
resolution PostScript versions are available at
http://www.th.physik.uni-frankfurt.de/~bender/nucl_struct_publications.html
or at ftp://th.physik.uni-frankfurt.de/pub/bender ), submitted to Phys. Rev.
